gpu: ion: Add ioctls for prefetching/draining pools

Multiple heaps in Ion are begining to pool large amounts of memory.
This gives a boost on average but clients may still take a hit
if the pool needs to be filled up again. Add an ioctl to give a
'hint' to add memory to the pool. Equivalently, add an ioctl to
drain some of the memory out of the pool to ennsure the memory
isn't hanging around for too long.

Change-Id: I2974322caa1520fd199d9cf2658f2fafceffb65c
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
gpu: ion: Add support for heap walking

Clients may wish to implement custom functions on a particular
heap ID. Add a generic interface to walk all the heaps available
and call a function on the particular heap ID.

Change-Id: I8b3de7a2de74cd9ea1873020ed00ee40100ce923
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
gpu: ion: Add support for getting the heap size of CMA regions

Currently, Ion heaps are able to allocate memory from appropriate
CMA regions without knowing the maximum size of the CMA region. New
Ion algorithms necessitate having the size of the heap available
for accounting. Add code to parse the devicetree to get the size of
the CMA region and associate it with the appropriate heap.

Change-Id: Ia9b560d496c76209c6116fa00f24f7b624c954f3
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>